The structures of two samples of Au nanoclusters supported on silica were studied by X-ray powder diffraction and X-ray absorption spectroscopy. The data relative to both techniques were analysed by an approach involving simulation based upon structural models and fitting. The X-ray powder diffraction model concerned a distorted face-centred cubic arrangement, with microstrains and parallel stacking faults in approximately spherical particles; as an alternative possibility, a linear combination of ordered face-centred cubic and non-crystalline (decahedral and icosahedral) particles was also taken into account. Both approaches gave calculated patterns closely resembling the experimental data. X-ray absorption spectra were fitted on the basis of face-centred cubic and non-crystalline arrangements. The best results were obtained by the face-centred cubic motif, while a simulation consisting in the superposition of face-centred cubic and non-crystalline components in the relative amounts determined by X-ray powder diffraction analysis gave a poor agreement with the experimental data. It was concluded that the good X-ray powder diffraction fitting obtained by linear combination of lognormal size-distributed face-centred cubic cubo-octahedral, decahedral and icosahedral contributions was a result of the flexibility of the basis set of functions, but that the complementary analysis of X-ray absorption data did not confirm the presence of a noteworthy fraction of non-crystalline particles.

Distorted FCC Arrangement of Gold Nanoclusters - a Model of Spherical Particles with Microstrains and Stacking Faults. A.Longo, A.Martorana: Journal of Applied Crystallography, 2008, 41[2], 446-55